1. Field of the Invention:
This invention relates to a method of controlling plant root growth. More specifically, the invention relates to a method of growing plants in the field wherein the root growth is controlled by the presence of a porous plastic bag.
2. Description of the Prior Art:
The basic concept of growing nursery stock, such as trees and the like, in containers is a well known commercial activity. However, the growing of trees in a container is efficient and economical only during the early period of the plant's development and is pragmatically restricted to containers no larger than about five gallons in size. Goodale, Toby W. and Whitcomb, Carl E. in a pair of articles entitled "Producing Woody Ornamental Shrubs in Containers, Costs of Production and Projected Profits", Ornamentals South, Vol. 2 (4); pages 20 through 25 (1980) and "Producing Woody Ornamental Shrubs in Containers, Influence of Fertility Level and Container Size", Ibid. Vol. 2 (3); pages 10 through 13 (1980), found that for most plants there is an optimum container size for growth of the particular plant with maximum economic return. Generally, it was found that to grow trees in containers more than two years was not economically feasible.
Contemporary improvements in the fundamental understanding of the nutrition of tree seedlings (and plants in general; for example, see U.S. Pat. No. 4,328,025) both in the propagation container and subsequent larger container have led to improved growth rates. Furthermore, recent developments in various aspects of air-root pruning of the tree seedling to destroy the tap root and stimulate a much more fibrous root system (such as described in co-pending U.S. application Ser. No. 309,085) further complicates the commercial economics of growing trees in containers in that the tree outgrows the container before the commercial distribution and sales take place. Thus, the also well known basic concept of growing plants such as trees and the like in containers until the young plants are mature enough to be transplanted to a field in a relatively compact or dense planting arrangement wherein their development continues until sold appears to be pragmatically a necessary commercial practice. This conclusion is further supported when considering the additional problems associated with the alternative of continuing the tree growth in a container. Namely, high summer temperatures reduce top and root growth principally due to the abnormally high soil temperatures in the container, while low winter temperatures may damage or kill roots even though the tops would have normally survived the winter if planted in the field and the vertical growth of trees frequently results in containers being blown over which means they must be straightened before watering and the like.
In contrast to the above problems, an article by Hogan, Charles and Whitcomb entitled "Producing Container Nursery Stock in the Field" Research Report P-705 of the Oklahoma Agricultural Experimental Station, Pages 43-44 (1974) observed that if plants could be produced in containers buried in the field, the surrounding soil would insulate the container from high summer temperatures and low winter temperatures, while holding plants upright at all times without staking. However, in order for such a system to function, a procedure must be developed to confine the roots to the growing medium in the container. Otherwise, the roots would grow out of the container into a large mass of soil, thus requiring digging and cutting before marketing. One of the major advantages to container grown stock is that most of the roots go with the top of the plant at marketing, thus no shock or adjustment occurs. It was felt that nearly one hundred percent retention of roots must be maintained if the field production with container system is to be considered.